The present invention relates generally to hybrid transmissions suitable for hybrid electric vehicles (HEVs) equipped with a prime mover such as an internal combustion engine (ICE) and a motor/generator, and more particularly to a hybrid transmission including a differential mechanism between a prime mover and a motor/generator for continuously variable speed control.
In recent years, there have been disclosed various hybrid transmissions. One such hybrid transmission has been disclosed in Japanese Patent Provisional Publication No. 2003-034154. The hybrid transmission includes a two-degree-of-freedom differential mechanism including a compound planetary gearset. The rotating members of the differential mechanism are connected to a prime mover such as an ICE as an input element, a drive train as an output element, and a pair of motor/generators for continuously variable speed control. In addition, an engine clutch is disposed between the ICE and an associated one of the rotating members of the differential mechanism for selective connection therebetween. The engine clutch is disengaged during a driving mode in which the vehicle is powered by only the motor/generators. This prevents drag resistance of the ICE during the ICE being inoperative.